A technique of taking an image of an object to be examined by optical coherent tomography (hereinafter abbreviated as OCT) using low coherent light has been researched and developed as a high-resolution bioinstrumentation measurement technique. In particular, a disease of a retina can be accurately detected by the use of a tomographic image of the retina. For this reason, this technique is practically applied to a fundoscopy apparatus, and is further being researched and developed for higher performance.
OCT is roughly classified into two types. One type is time domain OCT (TD-OCT) for changing the position where a tomographic image is taken, by controlling the optical path length of reference light. The other type is Fourier domain OCT (FD-OCT) that can acquire data in the eye depth direction (optical-axis direction of the optical system) by one operation.
Fourier domain OCT is further classified into two types. One type is spectral domain OCT (SD-OCT) that splits interference light with a diffracted grating and detects the split light with a line sensor. The other type is swept-source OCT (SS-OCT) using a light source capable of wavelength sweeping. At present, spectral domain OCT is in the mainstream because it takes less time to acquire data in the eye depth direction than time domain OCT. In the case of a fundoscopy apparatus, the position of the eye is displaced because of the motion, blink, or involuntary eye movement of the subject during measurement, and this causes misalignment of images. For this reason, there is a demand to reduce the measurement time. Patent Literature 1 (PCT Japanese Translation Patent Publication No. 2008-508068) discloses OCT in which a plurality of light spots are applied onto the eye to acquire a three-dimensional structure of the eye.